Zazen meditation is the main technique in Zen Buddhism. It's a mindfulness meditation with an emphasis on harmonizing breath, mind and body.
Zensters are really big on posture and building a physical foundation for meditation.
How to practice Zazen
1. Get in a sitting position. It can be any of the following.
Half lotus or full lotus (traditional in Zazen, but not medically sound for a lot of us)
Cross legged position on a meditation pillow. Try to get your knees below your butt, pointing downward.
Kneeling position while sitting on your heels.
In a chair with feet flat on the floor.
Whatever position you use, you want your tailbone firmly planted.
2. Stack your vertebrae all the way up, starting with the tail bone. When you get to the top, tuck in the chin a little bit. The head should feel like it's holding up the sky.
3. Close the mouth and teeth and allow them to relax. Point the tongue upward to the roof of the mouth. Push it back toward the throat as far as it will go comfortably.
4. Place your hands in the cosmic mudra. There's a video below with the visuals. The back of your right hand is on your lap below the navel with fingers pointing to the left. It is holding the fingers of your left hand which are pointing to the right. This is the base of your triangle. Your thumbs form the legs by joining together.
5. Defocus the eyes and close them only partially. Gaze downward at a 45 degree angle, focusing on nothing in particular.
6. Breathe through the nose. Relax the chest and let the abdomen do all the work. It should feel like the breath is being drawn in through the hara - the point a couple inches below the navel and a couple inches inward toward the body. Your focus is on the breath and the hara. These are all that exist.
7. If thoughts, emotions and other things distract you, let them be what they are. You are the ocean. They are the waves. They arise and they fall away. Be the impartial observer. They are not distracting you from the present moment. They exist in the present moment. Don't follow them and don't resist them. They just are.
8. Go back to the hara and the breath. If you get distracted, repeat steps 7 and 8.